Method for extruding explosives



Aug. 9, 1968 G. L. GRIFFITH METHOD FOR EXTRUDING EXPLOSIVES Filed Feb.10, 1964 3,255,773 Patented August 9, 1966 3,265,778 METHOD FOREXTRUDING EXPLOSIVES George L. Gritfith, Coopersburg, Pa., assignor toT'Z'Ojfil'l Powder Company, Allentown, Pa., a corporation of New YorkFiled Feb. 10, 1964, Ser. No. 343,844 Claims. (Cl. 264-3) This inventionrelates to a method and apparatus for the extruding of explosives, and,more particularly, to a process .for extruding a column of explosivecomposition for packaging, and to apparatus for carrying out thisprocess.

Recently, machinery has been made available which preforms an explosivecomposition, and this is then wrapped automatically in paper and crimpedat both ends, to produce a completed shell rather quickly, as comparedto the conventional procedure. This is an operation which producesshells of a fixed length. Due to certain mechanical restrictions, aswell as the investment cost of the machine, it is-not feasible tomanufacture finished shells having a length in excess of sixteen inches.Furthermore, the production rate of the machine is rather low.

The packaging of ammonium nitrate explosives presents a particularlysevere problem, from the standpoint of economics. Ammonium nitrate is acheap raw explosive material, which can be sensitized ratherinexpensively with fuel oil or some other form of carbon or carbonaceousmaterial to form what are termed the nitrocarbonitrates, which haveexplosive properties. Such mixtures can be brought in bulk to theexplosive site where they can be filled directly into small diameterbore holes having a diameter of as low as one inch, and then shot. Thistechnique poses a particularly difficult packaging problem, since, usingconventional explosive packaging procedures, it has been practicallyimpossible to package an inexpensive product in long lengths in apractical manner at a price sufliciently low to be competitive with theammonium nitrate-fuel oil bulk compositions which can be blown directlyinto the holes without packaging.

A further problem created by individual packaging of explosivecompositions arises from the necessity of propagating the charge fromone cartridge to another in the train. It has always been necessary touse an explosive composition in the package of such sensitivity that itis capable of shooting through a discontinuous column of explosive, thediscontinuity being brought about by the fact that for practicalpurposes explosives. are loaded normally in lengths of less than 24inches, and usually in lengths of 4 to 8 inches. Thus, an explosivecolumn in a small diameter hole of great length usually consists of fourto twelve sticks of powder, and the composition must necessarily havesufiicient sensitivity so that the detonating -wave will not die out asit travels through the discontinuous column of a plurality of sticks.Furthermore, a discontinuous column has less water resistance, since thepoint where two shells butt together is the first point at which waterdesensitizes the composition, presenting a zone through which the shockwave often fails to pass from one cartridge to the next. Obviously, ifit were possible to prepare an explosive column of great length, so thata continuous column could be loaded in the hole in place of adiscontinuous one, composed of a plurality of sticks in closejuxtaposition, it would be possible to use an explosive composition ofless sensitivity, since there would be no need to propagate theexplosive wave from one cartridge to another. Such a column would alsohave greater water resistance than the discontinuous one, since therewould be no point at which water could enter between one portion of theexplosive and another.

The packaging of gelled explosives has also presented a problem. Theseare diflicult to package in an efiicient manner so that they can be soldat a price which is competitive to ammonium nitrate-fuel oilcompositions. These difiiculties basically are due to the lack of amethod for packing long continuous tubes in an economical manner.

Casings of any desired length can be fabricated from plastic materials,such as regenerated cellulose, polypropylene, and the like. These areextruded in the desired diameter, and then filled by means of a longloading tube or nozzle through which the filling material is extrudedinto the casing. This method has been used for many years in themanufacture of sausages in the meat industry. However, it is not adaptedfor explosive compositions.

In the first place, explosive compositions of a consistency desirablefor such packages are virtually impossible to extrude. If the explosiveis fluid, it extrudes and packages easily, but the package isflimsy andlimp. If the explosive is semi-solid or solid, the packages areselfsupporting, but such consistencies can be extruded only at ratherhigh pressures, at which the composition may be unsafe to handle, due tothe pressures and heat generated, and which increase as the extrudedcolumn increases in length. As a practical matter, the limitingextrusion pres sure at which semi-solid explosives are safe to handle israther low, of the order of 40 psi, so that it is impossible to extrudemore than rather short columns, not much longer than normal lengthcartridges. This prevents reali zation of the real advantage ofextrusion: the preparation of explosive packages of practicallyunlimited length.

In according with the instant invention, apparatus is provided forextruding explosive compositions that permits extrusion of practicallyendless columns of explosive under moderate and safe extrusion pressuresbelow that at which detonation of the explosive would occur with aminimum of heat generation. It thus is possible to package semi-solidand plastic or gelled explosive compositions of extrudable consistencyin packages of any desired length and configuration.

The extrusion apparatus of the invention comprises an extruder blockhaving a lubricating means fitted therein to supply a film of lubricantbetween the explosive column being extruded and the walls of theextruder block. The term extruder block is used generically herein torefer to the extruder nozzle, die, barrel, tube or other means forconfining and shaping the material during extrusion. Such means can takethe form of a porous bearing or wall, a perforated plate, a wick orbrush applicator, or a seep opening or plurality of openings arranged todistribute lubricant over the column, preferably uniformly. Other meanswill be apparent from this description. The porosity and pore size willconform to the viscosity of the lubricant and the volume thereof to beapplied to the explosive column for the desired lubricating effect.

The lubricating means can be made of any material, preferably-longwearing, such as metal, for instance, stainless steel, brass, bronze,iron, steel or plastic, for instance, polyamide,polytetrafiuoroethylene, polyethylene, polypropylene, polystyrene,polyvinyl chloride, ureaformaldehyde or phenol-formaldehyde resin, orporcelain or ceramic material, or glass.

The lubricant can be applied by fluid pressure, as by a pump, or by gaspressure, or by a sufficient head of fluid pressure. Usually, the liquidis applied under a pressure at least equal to the extrusion pressure andpreferably at a pressure of from to 50 p.s.i. greater than the extrusionpressure, to ensure a continuous film formation at the interface.

Uniform and steady application of lubricant is best assured bymaintaining a feed flow of lubricant to and past the lubricating means,in contrast to a feed which dead-ends at the applicator. It is quitedifficult in the latter case to maintain a head of pressure adequate toensure a steady and uniform lubricant flow without an occasional breakthrough, as when extrusion pressure diminishes, for some reason, or whenfluid pressure builds up too high. A flow through, however, in themanner, for instance, shown in FIGURES 1 and 2, makes it possible tomaintain a constant head of pressure adequate to ensure a slow feed oflubricant over the normal range of extrusion pressure variationsencountered in operation.

The application means selected will have a pore size and flow capacityappropriate to deliver the required amount of lubricant to maintain asafe, low, extrusion pressure, below about 60 p.s.i., and this willdepend upon the friction developed bet-ween the explosive and the nozzlewall, the size of the column, the length of the nozzle, and the lengthof the column, as well as the type and viscosity of the lubricant.

The apparatus of the invention is useful for filling completed explosivepackages of any size and length, such as conventional cartridgecontainers, as well as stuffing or filling tubes of unlimited length, inthe manner of stufiing sausage casing, for which use the apparatus is ofespecial advantage. The extruded column is inserted into the enclosingwrapper shortly after leaving the extruder, and is then sealed thereinto close the package when a suitable length is filled. The container orpackage can be made of any desired material, such as paper or plastic,for example, polyvinyl chloride, polyethylene, or polypropylene.

Any type of extrusion equipment can be employed. The choice will dependupon the characteristics of the explosive composition being extruded.Conventional extruders comprising a feeding device and forming tube ordie, otherwise referred to as an extrusion nozzle or barrel, of thedesired configuration for shaping the explosive column, aresatisfactory. Such equipment will be provided with the lubricating meansin accordance with the invention for delivering the selected lubricantto the explosive.

The lubricant can be any appropriate liquid, and preferably a solventfor the explosive but inert to the material of which the extruder ismade. Water is the preferred lubricant, but lubricating oil, petroleumderivatives such as kerosene and fuel oil and hrydrocarbons of allkinds, silicone oils, dilute 0.5 to aqueous solutions of natural gums,such as guar-gum and karaya gum, and alkylene glycols such as ethyleneglycol, propylene glycol, and polyethylene glycol, and glycerine, arealso exemplary. Preferably, the lubricant does not upset the oxygenbalance of the composition, or else the lubricant is taken into account,if necessary, in formulating oxygen balance.

The lubricating effect is enhanced if the lubricant is applied hot,preferably at above 50 C., and optimally at a temperature at which thesurface of the explosive is softened or melted.

FIGURE 1 is a longitudinal section through an extruder feed and nozzleof the invention, showing an annular porous sintered metal bearing ringfor lubricating the column of explosive being extruded.

FIGURE 2 is a cross-sectional view of the extruder of 4 FIGURE 1, takenalong the line 22 and looking in the direction of the arrows.

The extruder of FIGURES 1 and 2 comprises a housing 1 made of stainlesssteel wit-h a rubber liner 2. A screw conveyor also of stainless steel 3is provided to feed explosive composition 7 to the stain-less steelextruder nozzle 4, where it is brought to the shape of a column 5.

The extruder nozzle 4 is provided at a point near housing 1 with alubricating means in the form of an annular porous sintered metalbearing 10, made of, say, stainless steel, Monel, bronze, ceramic orpolyte-trafiuoroethylene, and extending all the way around the innerwall of the extruder nozzle. The bearing is press-fitted into the top ofa stepped recess or groove 11 in the wall, where it rests against thestep 9, defining a space 12 between it and the base of the recess 11.Two circumferential grooves 17 and 18 extending all the way around thebearing receive O-rings 19 and 20 to ensure a leak-tight seal betweenbearing 10 and the step 9. A pair of ducts 13 and 14 provide access tospace 12 from the exterior of the extruder. It will be seen from FIGURES1 and-2 that the bearing '10 is thus spaced away from the base of therecess 11 throughout its periphery. Two fittings 15 and 16 are welded tothe outside wall of the extruder, and serve as a means for attachment ofa supply connection for delivery of lubricating fluid to the duct 13 andthence into the space 12, and withdrawal of excess lubricant via duct 14and fitting 16. In this manner, lubricating fluid is conveyed to allportions of the bearing 10, whence it can be expressed in the form of afilm of lubricating fluid, enveloping therein the extruded column 5 ofexplosive 7 passing through the nozzle, and lubricating its movementalong the inner wall of the extruder. The arrows show the course oflubricating fluid from the fitting 14 to the column .16 of extrudedexplosive in the extruder nozzle 4.

In operation, the explosive material 7, which is of a semi-solidconsistency, is poured into the hopper l, whence it is forced by thescrew conveyor 3 into the extruder nozzle 4. The rubber lining 2 on thewalls of the hopper 1 provides a desirable resiliency, to avoid shock tothe ex plosive under the force of the impeller 3.

The explosive 7 acquires the columnar configuration of the nozzle 4 assoon as it enter the nozzle, filling it completely and forming a column5. As the column 5 is forced through the nozzle, under a pressure of say20 p.s.i., by the impeller 3, it passes the bearing 10, and thereacquires a film of lubricant liquid such as water fed through thebearing 10 under a pressure of say 30 to 40 p.s.i. applied by a fluidpump (not shown) in the line supplying fluid to the fitting 15. Surpluswater is withdrawn via duct 14 and fitting 16. The explosive column 5 isnow coated with a very thin film of lubricant liquid at the interfacebetween the explosive and the inner wall of the extruder 4. This film isextremely thin, of the order of 0.0001 inch to 0.05 inch. As a result ofapplication of the lubricating film, the pressure of extrusion of thecolumn 5 is greatly reduced, and the column length extrudable thereby ata given extrusion pressure correspondingly increased. Whereas a columnlength of approximately 12 inches, for example, may be the limit ofwhich the extruder is capable, at 60 p.s.i., without development ofexcessive extrusion pressures and heat generation, due to frictionbetween the wall of the extruder and the explosive composition, thepresence of the bearing 10 and the lubricating film (water) can increasethe length extrudable at from A to A; of the I pressure needed toextrude 12 inches with no lubrication to from to inches and more. Thus,the lubricating film makes it possible to avoid high extrusionpressures, and to keep extrusion pressure below the detonation limit ofthe explosive composition.

The following examples, in the opinion of the inventors, represent thebest embodiments of their invention.

Ingredients:

EXAMPLE 1 An explosive mixture of semi-solid consistency was preparedusing dry milled nitrostarch, fine grained ammonium nitrate,fine-grained sodium nitrate, flake aluminum, and the additionalingredients noted in the table below. The nitrostarch and mixed nitrateswere thoroughly blended, and there was then added the zinc oxide, flakealuminum, guar gum, and then the oil and water. The proportions of thefinal explosive composition were as follows:

Percent Nitrostarch 27.00 Grained ammonium nitrate 47.25 Grained sodiumnitrate 10.75 Flake aluminum 2.50 Guar gum 2.50 Oil No. 5 1.00 Zincoxide 1.00 Water 8.00

This composition was quite stiff, and was easily extruded through long1% inch diameter extrusion nozzles of the type shown in FIGURES 1 and 2at an extrusion pressure of 25 p.s.i. using water as the lubricant undera pressure of 35 p.s.i., into a tubular casing ten feet long and twoinches in diameter, made of polyethylene film, which was rolled up as itwas filled.

EXAMPLE 2 An explosive mixture of semi-solid consistency was formulatedusing milled nitrostarch, ammonium nitrate, and sodium nitrate. Theammonium nitrate and sodium nitrate were both fine-grained. Thesematerial were mixed thoroughly and there were then added zinc oxide,

flake aluminum, guar gum, sodium carboxymethyl cellulose, and woodflour, after which the water was added. The proportions of the finalexplosive mixture were as follows:

This mixture had the consistency of a gelled-oil, and was easilyextruded through long 1 inch diameter nozzles of the type shown inFIGURES 1 and 2 at an extrusion pressure of 25 p.s.i. using water as thelubricant under a pressure of 35 p.s.i., into a polyethylene tubularcasing 1% inches in diameter and twenty feet long, which was rolled upas it was filled.

EXAMPLES 3 TO 5 Three explosive mixtures of semi-solid consistency wereprepared using as the sensitizer pentaerythritol tetranitrate ortrimethyloltrinitrate, with mill ammonium nitrate, mill sodium nitrate,flake aluminum, and the additional ingredients noted in the table below.The sensitizer and mixed nitrates were thoroughly blended, and therewere then added the zinc oxide, flake aluminum, guar gum, sodiumcarboxymethyl cellulose and wood flour, and then the water. Theproportions of the final explosive composition were as follows:

Example Number Ingredient Percent Percent Pcrcrnt 'Irimethylolethnnetrinitmte. .6 Pentaerythritol tetrnnitrnto 24. (l 12. l) Ammoniumnitrate, mill 48. 4 61. 9 72. 5 Mill sodium nitrate 13. 5 Flakealuminum. 2.0 2.0 '2. 0 Jaguar guar gum 1.0 1.0 1.0 Sodium carboxymethylcellulo O. 6 0. 6 0. (1 Wood flour 1.5 1.5 1. 5 Zinc oxide 1.0 1.0 1.0Water 7. 4 7. 4 7. 4

100. 0 100.0 100.0 Density 1. 53 1. 23 1. 26

These compositions were quite stiff, and were easily extruded throughlong one inch diameter extrusion nozzles of the type shown in FIGURES 1and 2 at an extrusion pressure of 25 p.s.i. using ethylene glycol as thelubricant under a pressure of 35 p.s.i., into cartridges 48 inches longand 1% inches in diameter, made of heavy cardboard, 0.082 inch inthickness, and the cartridges were then covered with cardboard caps.

EXAMPLES 6 AND 7 Example Number Ingredient Composition B Ball powder(Olin WC 820) Mill ammonium nitrate. Mill sodium nitrate 1 Flakealuminum Jaguar 100 guar gum Sodium carboxymethyl cellulose Loadingdensity... Sensitivity in 1% pipe 1 Pellets averaging about 1.25 mm. indiameter.

I Double base nitrocellulose powder. 9 3 gm. PETN.

These mixtures had the consistency of a gelled oil, and were easilyextruded through long one inch diameter nozzles of the type shown inFIGURES l and 2 at an extrusion pressure of 25 p.s.i. using water as thelubricant under a pressure of 35 p.s.i., into open-ended cardboardcartridges 1% inches in diameter and two feet long. The cartridges thenwere closed with cardboard covers.

EXAMPLES 8 TO 10 Three explosive mixtures of semi-solid consistency wereprepared using trinitrotoluene and ethylene glycol dinitrate assensitizers, mill ammonium nitrate, mill sodium nitrate, flake aluminum,and the additional ingredients noted in the table below. Thetrinitrotoluene. and/or ethylene glycol dinitrate and mixed nitrateswere thoroughly blended, and there were then added the zinc oxide, flakealuminum, guar gum, sodium carboxymethyl 7 cellulose, wood flour, andthen the water. The proportions of the final explosive composition wereas follows:

- Example Number Ingredient Perce Percent Percent Trinitrotoluene, 35mesh 24. 6 20. 14. 1 Ethylene glycol dinitrate 10. 6 Mill ammoniumnitrate 13.0 48. 0 41. 0 Mill sodium nitrate..- 4B. 9 20.0 20. 9 Flakealuminum 2. 0 2. 0 2. 0 Jaguar 100 gunr gum 1. 0 1. 0 1. 0 Sodiumcarboxymetliyl cellul 0. 6 0.6 0. 6 Wood flour 1.5 1. 1.5 Zinc oxide 1.01.0 1.0 Water 7. 4 7. 4 7. 4

' 100. 0 100. 0 100.0 Loading density 1. 44 1. 34 1. 53

Sensitivity in 1% pipe 1 N o. 8 cap. These compositions were quitestiff, and were easily extruded through long one inch diameter extrusionnozzles of the type shown in FIGURES l and 2 at an extrusion pressure of25 p.s.i. using water as the lubricant under a pressure of 35 p.s.i.,into polypropylene film casings feet long and 1% inches in diameter. Theopen ends of the casings were sealed, and the filled lengths rolled up.

EXAMPLES 11 TO '15 Five explosive mixtures of semi-solid consistencywere formulated using dry milled nitrostarch, ammonium nitrate, andsodium nitrate. The ammonium nitrate and sodium nitrate were bothfine-grained. These materials were mixed thoroughly, and there were thenadded zinc oxide, flake aluminum, guar gum, sodium carboxymethylcellulose, and wood flour, after which the water was added. Theproportions of the final explosive mixture were as follows:

These mixtures had the consistency of a gelled oil, and were easilyextruded through long one inch diameter nozzles of the type shown inFIGURES l and 2 at an extrusion pressure of 25 p.s.i. using water as thelubricant under a pressure of p.s.i., into open-ended cardboardcartridges 1% inches in diameter and two feet long.

The following is claimed:

1. A process for extruding an explosive composition of extrudableconsistency, comprising a primary explosive and sensitive to detonationat pressures in excess of about p.s.i., and at elevated temperatures, inorder to minimize pressure and heat-generation during extrusion,comprising confining said explosive compos-itior within a passage ofrelatively small diameter to form an explosive column of substantiallength therein, and moving the explosive column along the passage byapplication of a pressure below about 60 p.s.i. to one end thereof,while applying a film of liquid lubricant at a pressure within the rangefrom the extrusion pressure to 50 p.s.i. greater than the extrusionpressure, between the surface of the explosive column and the wall ofthe passage, whereby the explosive composition is extruded safely at apressure and temperature below that at which detonation of the explosiveoccurs.

2. A process in accordance with claim 1 in which the liquid lubricant iswater.

3. A process in accordance with claim 1 in which the liquid lubricant isethylene glycol.

4. A process in accordance with claim 1 in which the liquid lubricant isapplied at a temperature of at least 50 C.

-5. A process in accordance with claim 1 in which the liquid lubricantis a solvent for the explosive composition being extruded.

Example N umber Ingredient Percent Percent Percent Percent PercentNitrostarch r 40. 0 Pentnerythritol tetranitrat G. 0 9. 0 12. 0 40. OMill ammonium nitrute 79.0 74. 5 57. 0 24. 0 35.0 Mill sodium nitrate 7.5 15. 0 15. 0 Flake aluminum 5.0 1.0 0. 5 1.0 0. 5 Jaguar guar gum 1.01.0 3. 5 3. 6 0. 1. 5 1. 5 0 5. 0 l. 0 0. 5 .0 1. 0 1.0 1. 0 5 12. 0 12.0 8. 5

2 g. PETN. 10 g. PETN. 111-21) g. PEIN. 4 No. 2 cap. 5 No. 8 cap.

References Cited by the Examiner UNITED STATES PATENTS LEON D. ROSDOL,Primary Examiner. L. DEWAYNE RUTDEDGE, REUBEN EPSTEIN,

Examiners.

1. A PROCESS FOR EXTRUDING AN EXPLOSIVE COMPOSITION OF EXTRUDABLECONSISTENCY, COMPRISING A PRIMARY EXPLOSIVE AND SENSITIVE TO DETONATIONAT PRESSURES IN EXCESS OF ABOUT 60 P.S.I., AND AT ELEVATED TEMPERATURES,IN ORDER TO MINIMIZE PRESSURE AND HEAT-GENERATION DURING EXTRUSION,COMPRISING CONFINING SAID EXPLOSIVE COMPOSITION WITHIN A PASSAGE OFRELATIVELY SMALL DIAMETER TO FORM AN EXPLOSIVE COLUMN OF SUBSTANTIALLENGTH THEREIN, AND MOVING THE EXPLOSIVE COLUMN ALONG THE PASSAGE BYAPPLICATION OF A PRESSURE BELOW ABOUT 60 P.S.I. TO ONE END THEREOF,WHILE APPLYING A FILM OF LIQUID LUBRICANT AT A PRESSURE WITHIN THE RANGEFROM THE EXTRUSION PRESSURE TO 50 P.S.I. GREATER THAN THE EXTRUSIONPRESSURE, BETWEEN THE SURFACE OF THE EXPLOSIVE COLUMN AND THE WALL OFTHE PASSAGE, WHEREBY THE EXPLOSIVE COMPOSITION IS EXTRUDED SAFELY AT APRESSURE AND TEMPERATURE BELOW THAT AT WHICH DETONATION OF THE EXPLOSIVEOCCURS.